This invention relates to improvements in a pulse counting-rate meter for use in radioactive measurements or the like and more particularly to a pulse counting-rate meter having a high time constant and high accuracy.
Conventional counting-rate meters for use in radioactive measurements or the like have been of the type in which an electric charge having a predetermined magnitude is supplied to a parallel circuit including a resistor and a capacitor for each input pulse to develop a voltage across the resistor due to the mean current for the supplied charges which voltage is measured. In that type of counting-rate meter the resistor has been the element which determines the system sensitivity, and therefore the accuracy of measurement has been limited by the stability of the magnitude of resistance of that resistor. In the radioactive measurements it is required to increase the time constant as determined by a resistor and a capacitor such as above described in order to decrease the statistical error, and accordingly high resistance elements have been inevitably employed. This is because plastic film type capacitors having a high capacitance and low in leakage current is not commercially available. Although a high resistance of magnitude of about 10.sup.9 ohms is required to be used in order to provide a time constant of from about 1 to 10 minutes, such resistors can only have a stability of resistance magnitude of at most 1%. Thus counting-rate meters including such resistors can only have an accuracy of measurement on the order of at most 1%.
Accordingly it is an object of the present invention to provide a new and improved counting-rate meter having both a time constant and high accuracy wherein the disadvantages of the prior art meters are eliminated.